Stretchable anti-buckling coiled-sheet stent

ABSTRACT

A stent-graft having an exo-skeleton attached to a tubular graft, the tubular graft having a peripheral wall defining a lumen therein extending between first and second ends. The exo-skeleton may assume contracted and enlarged conditions, and includes one or more serpentine elements, each extending both peripherally and axially along at least a portion of the peripheral wall. Coiled-sheet stents are provided on the ends of the tubular graft for anchoring the ends within a body passage. Each serpentine element is a zigzag structure extending peripherally about the peripheral wall, with a plurality of serpentine elements distributed axially along the peripheral wall. The serpentine elements are individually attached to the peripheral wall and/or connector elements may extend between adjacent serpentine elements. Alternatively, each serpentine element may define a generally sinusoidal shape extending axially along the peripheral wall. The tubular graft may have a bifurcated end from which a tubular graft extension segment may extend and to which a docking limb may be attached. A plurality of serpentine elements may also be attached to the extension segment and the docking limb.

FIELD OF THE INVENTION

[0001] The present invention relates generally to prostheses forimplantation with body lumens, and more particularly to a stent-grafthaving a flexible exo-skeleton attached to a tubular graft.

BACKGROUND

[0002] Graft prostheses are often implanted within blood vessels,particularly the aorta or other arteries, which may be subject toaneurysm formation and/or severe atherosclerotic disease which mayinvolve multiple stenoses. For example, an aortic aneurysm may developin a patient, for example, within the abdominal aorta at the aorto-iliacbifurcation, requiring treatment before the vessel wall ruptures. Torepair a blood vessel damaged by such an affliction, a procedureinvolving use of a graft prosthesis is generally performed.

[0003] A number of graft prostheses have been suggested that include atubular graft attached to a stent. The tubular graft may be abiocompatible porous or nonporous tubular structure to which a stentstructure, such as a wire mesh, may be attached. The stent structure maybe biased to assume an enlarged configuration corresponding to a targettreatment site, but may be constrained in a contracted condition tofacilitate introduction into a patient's vasculature. The graftprosthesis may be percutaneously introduced in the contracted condition,advanced to a treatment site within a blood vessel, and released toassume the enlarged condition and repair and/or bypass the treatmentsite.

[0004] One problem often associated with such prostheses is effectivelysecuring the tubular graft at the treatment site. The released graftprosthesis may not sufficiently engage the vessel wall adjacent thetreatment site, possibly resulting in the graft prosthesis moving afterimplantation, which may expose the damaged vessel wall. Plasticallydeformable expandable stent structures may be provided to attempt tomore directly control the engagement between the graft prosthesis andthe vessel wall. Such expandable structures, however, may require theuse of a balloon or other expandable member to expand the stentstructure to the enlarged condition, which may introduce risks of unevenstent structure expansion and/or balloon rupture.

[0005] In addition to plastically deformable stents, coiled-sheet stentstructures have been suggested. Coiled-sheet stents may provide enhancedanchoring within the blood vessel because the size of the fully expandedstent may be more precisely controlled. A coiled-sheet stent, however,may be substantially rigid transverse to its longitudinal axis,potentially resulting in a less flexible graft prosthesis, which may notbe implanted effectively in tortuous anatomical conditions.

[0006] Therefore, there is a need for an improved stent-graft that mayprovide improved flexibility, while still providing substantialanchoring within a blood vessel.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to a stent-graft having anexo-skeleton attached to a tubular graft. In accordance with one aspectof the present invention, a stent-graft is provided that includes atubular graft having a peripheral wall defining a periphery and a lumentherein, the lumen extending axially between first and second ends ofthe tubular graft. An exo-skeleton is attached to the peripheral wall,the exo-skeleton including one or more serpentine elements, eachserpentine element extending both peripherally, i.e., in a manner whichgenerally surrounds the wall which may be circular, elliptical or othersuitable configuration, and axially along at least a portion of theperipheral wall. A stent is provided on the first and/or second ends forsubstantially anchoring the ends within a body passage.

[0008] In a preferred form, each serpentine element is a zigzagstructure extending peripherally about the peripheral wall of thetubular graft. More preferably, a plurality of serpentine elements aredistributed axially along the peripheral wall for providing articulationof the tubular graft between adjacent serpentine elements. Theserpentine elements may be individually attached to the peripheral walland/or the serpentine elements may be connected to one another by one ormore connector elements extending between adjacent serpentine elements.

[0009] In another preferred form, each serpentine element defines agenerally sinusoidal shape extending axially along the peripheral wall.Preferably, a plurality of serpentine elements may distributedsubstantially evenly about the periphery of the peripheral wall. Each ofthese serpentine elements preferably includes substantially transverseperipheral elements, adjacent transverse peripheral elements beingconnected by alternating curved elements, thereby defining the generallysinusoidal shape.

[0010] The exo-skeleton of the stent-graft is preferably directablebetween a contracted condition for facilitating introduction within abody passage and an enlarged condition for deployment within the bodypassage. The exo-skeleton may substantially support the tubular graft tohold the lumen of the tubular graft substantially open in the enlargedcondition. In a preferred form, the exo-skeleton is radiallycompressible to the contracted condition and biased to assume theenlarged condition. Alternatively, the contracted condition of theexo-skeleton may be achieved by flattening and circumferentially rollingthe exo-skeleton.

[0011] The tubular graft may be provided from a polymeric material, suchas polyester, polytetrafluorethaline, dacron, teflon, and polyurethane.The exo-skeleton may be attached to the tubular graft by sutures,staples, wires, or an adhesive, or alternatively by thermal bonding,chemical bonding, and ultrasonic bonding. The exo-skeleton may be formedfrom a metallic material, such as stainless steel or Nitinol, and may bea flat-coiled sheet with the one or more serpentine elements formedtherein, or a wire formed into a serpentine shape.

[0012] In alternative forms, the first and second ends of the tubulargraft may have similar cross-sections, or the first end of the tubulargraft may have a cross-section that is substantially smaller than across-section of the second end of the tubular graft. In addition, theexo-skeleton may be attached to an exterior surface of the tubulargraft, to an interior surface of the tubular graft, or embedded in thewall of the tubular graft.

[0013] In accordance with another aspect of the present invention, astent-graft is provided for placement within a bifurcation that includesa first tubular graft segment having a first end and a second bifurcatedend, the first tubular graft segment having a first peripheral wall. Asecond tubular graft segment extends from the second bifurcated end, thesecond tubular graft segment having a second peripheral wall. Anexo-skeleton is attached to at least one of the first and secondperipheral walls, the exo-skeleton including one or more serpentineelements, each serpentine element extending both peripherally andaxially along at least a portion of the respective peripheral wall towhich it is attached.

[0014] A coiled-sheet stent may be provided on the first end forsubstantially anchoring the first end within a body passage. Similarly,a coiled-sheet stent may be provided on the second tubular graft segmentopposite the second end of the first tubular graft segment.

[0015] Preferably, the stent-graft also includes a third tubular graftsegment attachable to the second bifurcated end, the third tubular graftsegment having a third peripheral wall. The exo-skeleton also mayinclude one or more serpentine elements attached to the third peripheralwall.

[0016] Thus, a stent-graft in accordance with the present invention mayhave a substantially flexible region that may conform substantially tothe anatomy of a treatment site. Preferably, the flexible region isdefined by an exo-skeleton attached to a tubular graft that includes oneor more serpentine elements. The serpentine elements may facilitatearticulation between adjacent serpentine elements, and/or may besufficiently resilient and flexible to allow articulation, compressionand/or expansion of the serpentine elements themselves.

[0017] Preferably, the stent-graft also includes sealing members,preferably coiled-sheet stents, attached to the ends of the tubulargraft for substantially sealing and/or anchoring the ends of the tubulargraft proximate the treatment site. Thus, the stent-graft mayaccommodate tortuous anatomy while still providing effective sealing andanchoring within a body passage.

[0018] Other objects and features of the present invention will becomeapparent from consideration of the following description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 shows a perspective view of a stent-graft with exo-skeletonin accordance with the present invention.

[0020]FIG. 2 is a side view detail of the stent-graft of FIG. 1, showinga first preferred embodiment of a plurality of serpentine elementsdefining the exo-skeleton.

[0021]FIGS. 3A and 3B are cross-sections of the stent-graft of FIG. 1,taken along line 3-3, and showing the stent-graft in contracted andenlarged conditions, respectively.

[0022]FIG. 4 is a perspective view of an alternative embodiment of aserpentine element attachable to a tubular graft (in phantom).

[0023] FIGS. 5A-5D are end views of a stent-graft in accordance with thepresent invention, showing a method for rolling the stent-graft into acontracted condition.

[0024]FIG. 6 is a perspective view of another embodiment of astent-graft, having a tapered configuration.

[0025]FIG. 7 is a perspective view of still another embodiment of astent-graft, having a bifurcated main segment, an extension segment andan attachable docking limb.

[0026]FIG. 8 is a cross-sectional view of an abdomen, showing a methodfor implanting a stent-graft across a bifurcation for treating ananeurysm at the bifurcation.

[0027]FIG. 9 is a side view of a fully stretchable stent for use with astent-graft in accordance with the present invention.

[0028]FIGS. 10A and 10B are end and side views, respectively, of a stentwith anti-buckling segment.

[0029]FIGS. 11A and 11B are side and perspective views, respectively, ofa stent with stretchable ends.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Turning now to the drawings, FIG. 1 shows a first preferredembodiment of a stent-graft 10 in accordance with the present inventionthat includes a tubular graft 12, an exo-skeleton 14, and first andsecond coiled-sheet stents 16, 18. The tubular graft 12 has first andsecond ends 20, 22 defining a longitudinal axis 24 therebetween and aperipheral wall 26 defining a periphery 28 and a lumen 30 therein. Thetubular graft 12 may be formed from a variety of biocompatiblematerials, preferably a polymeric material, such as polyester,polytetrafluorethaline, dacron, teflon, and polyurethane.

[0031] The exo-skeleton 14 is attached to the peripheral wall 26 andincludes a plurality of serpentine elements 32. The exo-skeleton 14 maybe formed from a variety of semi-rigid materials, preferably abiocompatible metallic material, such as Nitinol or stainless steel. Thematerial may be resiliently deformable, may exhibit shape memoryproperties and/or may be plastically deformable, as described furtherbelow, to facilitate articulation of the stent-graft 10, and/or thecollapse and/or expansion of the exo-skeleton 14 between a contractedcondition and an enlarged condition. The exo-skeleton 14 may be formedfrom flat sheet material having the individual serpentine elements 32etched, cut or otherwise formed from the sheet material. Alternatively,the exo-skeleton 14 may be formed from wire-like materials, for example,by forming each serpentine element 32 from a single strand of wire.

[0032] The exo-skeleton 14 may be attached either to the exterior of theperipheral wall 26, to the interior of the peripheral wall 26, oralternatively embedded in the peripheral wall 26, with the term“exo-skeleton” being intended to include any of these locations and notto be limited to one location over another. The exo-skeleton 14 may beattached by mechanical fasteners, such as sutures, wires, staples, andthe like, by an adhesive, or by a bonding process, such as thermalbonding, chemical bonding, or ultrasonic bonding.

[0033] Each serpentine element 32 extends both “peripherally” and“axially” along at least a portion of the peripheral wall 26.“Peripherally” refers to each serpentine element 32 extending in amanner which generally surrounds the peripheral wall 26 which preferablymay be circular or elliptical, e.g., generally around the circumferenceor other periphery of the peripheral wall 26, while “axially” refers tothe serpentine element 32 extending along the peripheral wall 26generally parallel to the longitudinal axis 24. Thus, each serpentineelement 32 defines a generally “zigzag” shape made up, for example, ofabrupt “z” and/or rounded “U” shaped elements integrally connectedtogether.

[0034] In a first preferred form, shown in FIGS. 1 and 2, the serpentineelements 14 are defined by a plurality of zigzag elements, includinggenerally straight axial regions 32 a and curved peripheral regions 32b, integrally formed together that extend substantially peripherallyabout the peripheral wall 26. The serpentine elements 32 consequentlyprovide a multi-cellular exo-skeleton 14 that may facilitatearticulation between adjacent serpentine elements 32 when thestent-graft 10 is directed substantially transversely with respect tothe longitudinal axis 24.

[0035] In one form, the serpentine elements 32 are connected byconnector elements 34, which preferably extend substantially axiallybetween adjacent serpentine elements 32. The connector elements 34 maybe formed, etched or cut, when the serpentine elements are formed from aflat sheet, or the connector elements 34 may be strands of wire attachedto the serpentine elements 32 in a conventional manner. Alternatively,the serpentine elements 32 may be separate structures that areindividually attached to the peripheral wall 26 of the tubular graft 12.

[0036] The coiled-sheet stents 16, 18 may be attached to the respectiveends 20, 22 of the tubular graft, preferably to the interior of theperipheral wall 26, although alternatively the coiled-sheet stents 16,18 may be provided as separate components from the tubular graft 12. Thecoiled-sheet stents 16, 18 may expand automatically, but are preferablymechanically expandable, e.g., they may be ratchetable to largerdiameters, for example, using a balloon or other expandable member (notshown).

[0037] The coiled-sheet stents 16, 18 may have a stretchable design, astretchable anti-buckling segment, and/or a stretchable crowning end.For example, as shown in FIG. 9, a fully stretchable coiled-sheet stent410 is shown that is formed from a substantially flat mesh structure 412defining individual resilient mesh elements 420 and having teeth 414along a side edge 416 thereof for being received within the meshelements 420. The mesh structure 412 may be rolled or coiled to define alongitudinal axis 418 and a circumference or periphery (not shown) in aplane substantially perpendicular to the longitudinal axis 418. The meshstructure 412 may be formed from a plastically deformable material, suchas stainless steel.

[0038] In a preferred form, however, the mesh structure 412 is formedfrom Nitinol or similar shape memory material, which has, for example,been polished and/or heat treated. In a free-stress state, e.g., theaustenitic phase, the mesh elements 420 preferably define a “stretched”condition, i.e., expand about the periphery of the mesh structure 412such that the mesh structure 412 is biased to assume an enlarged size,e.g., substantially similar to the cross-section of a vessel withinwhich the stent 410 is to be implanted. The mesh elements 420 may adoptan “unstretched” configuration, i.e., may be compressed about theperiphery of the mesh structure 412, such that the mesh structure 412adopts a substantially reduced size. This may be achieved bytransforming the Nitinol material of the mesh structure 412 to amartensitic phase, for example, upon cooling after heat treatment. Thestent 410 may then be rolled and/or collapsed to a reduced deliveryprofile for attachment to a stent-graft, such as those described herein.

[0039] When the stent 410 is implanted within a blood vessel, the meshstructure 412 may stretch or return to its stress-free state, e.g., theaustenitic phase, and expand to engage the vessel wall. If radialpressure is applied to the stent 410 by the vessel, the mesh elements420 may be compressed about the periphery, thereby allowing the stent410 to recoil and substantially eliminate the likelihood of the stent410 buckling, as may occur when a conventional coiled-sheet stent issubjected to substantial radially compressive forces.

[0040] Turning to FIGS. 10A and 10B, another embodiment of acoiled-sheet stent 510 is shown that has a stretchable anti-bucklingsegment 512 formed from a mesh structure that is attached to acoiled-sheet portion 514. The coiled-sheet portion 514 includes teeth516 along a side edge 518 and may be rolled or coiled to defineoverlapping inner and outer longitudinal sections 524, 526, alongitudinal axis 520 and a periphery 522 such that the anti-bucklingsegment 512 extends axially, i.e., substantially parallel to thelongitudinal axis 520. Similar to the previous embodiment, theanti-buckling segment 512 may be formed from Nitinol, which may be heattreated and stretched, and then cooled and unstretched. The axiallyoriented anti-buckling segment 512 facilitates the entire stent 510recoiling when subjected to radially compressive forces by providingmesh elements 524 which may be compressed about the periphery 522, asdescribed above. Thus, the stent 510 may combine the benefits of both acoiled-sheet stent, which is generally incompressible about itsperiphery, and a stretchable stent structure.

[0041] Turning to FIGS. 11A and 11B, another embodiment of a stent 610is shown that includes an anti-buckling segment or “crowning end” 616 onone end 614 of a coiled-sheet portion 612. The coiled-sheet portion 612and anti-buckling segment 616 include teeth 618 a, 618 b along a sideedge 620 thereof, and may be rolled to define a longitudinal axis 622and a perimeter 624. The anti-buckling segment 616 is preferablypolished, heat treated into a desired shape, cooled and unstretched, andthen coiled to its collapsed and rolled delivery profile. After beingimplanted, mesh elements 626 in the anti-buckling segment 616 may becompressed when the stent 610 is subjected to radially compressiveforces, similar to the embodiments described above, thereby allowing theends of the stent 610 to become tapered. Alternatively, the end 628 ofthe anti-buckling segment 616 may be flared outward (not shown) tothereby partially recoil under radially compressive forces such that thestent adopts a substantially uniform size upon implantation within ablood vessel.

[0042] The coiled-sheet stents 16, 18 may also includeoutwardly-oriented hooks or barbs (not shown) for enhancing anchoring ofthe stent-graft 10 within a body passage. Pro-thrombotic material (notshown) may be provided on the exterior surfaces of the coiled-sheetstents 16, 18, or alternatively on the ends 20, 22 of the tubular graft12, to enhance sealing against the wall of the body passage. Additionalinformation on coiled sheet stents appropriate for use with astent-graft in accordance with the present invention may be found inU.S. Pat. Nos. 4,577,631 issued Mar. 25, 1986 in the name of Kreamer,5,007,926 issued Apr. 16, 1991 in the name of Derbyshire, 5,158,548issued Oct. 28, 1992 in the name of Lau et al., Re 34,327 reissued Jul.27, 1993 in the name of Kreamer, 5,423,885 issued Jun. 13, 1995 in thename of Williams, 5,441,515 issued Aug. 15, 1995 in the name of Khosraviet al., and 5,443,500 issued Aug. 22, 1995 in the name of Sigwart. Thedisclosures of these references and any others cited therein areexpressly incorporated herein by reference.

[0043] Turning to FIGS. 3A and 3B, the stent-graft 10 may be radiallycompressible from an enlarged condition, shown in FIG. 3B, to acontracted condition, shown in FIG. 3A. In a preferred form, theexo-skeleton 14 may be resiliently biased to assume the enlargedcondition, but may be constrained in the contracted condition tofacilitate introduction of the stent-graft 10 into a patient'svasculature.

[0044] For example, the stent-graft 10 may be constrained in thecontracted condition, and percutaneously introduced into a blood vessel(not shown). The stent-graft 10 may be advanced to a target treatmentsite, e.g., within the aorta or other blood vessel (not shown), anddeployed, with the exo-skeleton 14 automatically expanding to theenlarged condition. The coiled-sheet stents 16, 18 may then be expandedto a desired size to substantially engage and anchor the ends 20, 22 ofthe tubular graft 12 in place proximate the treatment site.Alternatively, if the coiled-sheet stents 16, 18 are provided asseparate components (not shown), they may be subsequently deployed andexpanded to anchor the ends 20, 22 of the previously deployed tubulargraft 12.

[0045] The exo-skeleton 14 may be retained in the contracted conditionsimply by applying a radial compressive force to the stent-graft 10 andconstraining the stent-graft 10, for example, within a sheath.Alternatively, if the exo-skeleton 14 is formed from Nitinol, themartensitic properties of the Nitinol may be used to substantiallyretain the stent-graft 10 in the contracted condition after beingradially compressed. The “zigzag” configuration of the serpentineelements 32 of the exo-skeleton 14 may facilitate substantially uniformradial compression of the stent-graft 10 when it is subjected toradially compressive forces, as shown in FIG. 3A, thereby minimizing therisk of localized stress in the exo-skeleton 14 and/or the tubular graft12.

[0046] When the exo-skeleton 14 automatically assumes the enlargedcondition, the serpentine elements 32 preferably substantially expandand support the peripheral wall 26 of the tubular graft 12, therebymaintaining the lumen 30 substantially open and unobstructed, as may beseen in FIG. 3B, for example, to facilitate blood flow through thetreatment site being repaired. In an alternative form, the exo-skeleton14 may be initially formed in the contracted condition, but may beplastically deformable to the enlarged condition, for example, using aballoon or other expandable member after the stent-graft 10 has beendeployed at the treatment site, as will be appreciated by those skilledin the art.

[0047] The multi-cellular configuration provided by the plurality ofserpentine elements 32 of the exo-skeleton 14 may facilitate thestent-graft 10 conforming substantially to tortuous anatomy duringadvancement and/or upon deployment at a treatment site. If thestent-graft 10 is subjected to substantially transverse forces, forexample, when it is directed around a tightly curved region of a bloodvessel, the stent-graft 10 may be easily articulated between adjacentserpentine elements 32 to conform to the shape of the blood vessel. Inaddition, the zigzag elements of each serpentine element 32 may beresiliently deformable, thereby further facilitating conformance withlocal anatomic conditions. Thus, a stent-graft 10 in accordance with thepresent invention may have a substantially flexible intermediate region29 extending between substantially rigid anchoring stents 16, 18. Theintermediate region 29 may allow the tubular graft 12 to conform to theanatomy of the treatment site, while the exo-skeleton 14 substantiallysupports the tubular graft 12 to prevent collapse or buckling.

[0048] Turning to FIG. 4, another preferred form of an exo-skeleton 114is shown that includes one or more serpentine elements 132 attached tothe peripheral wall 126 of a tubular graft 112 (in phantom) that extendsubstantially axially along the longitudinal axis 124 of a stent-graft110. Each serpentine element 132 preferably defines a generallysinusoidal shape extending substantially axially along the peripheralwall 126, and includes substantially transverse peripheral elements 134,with adjacent peripheral elements 134 being connected by alternatingcurved elements 136 to define the generally sinusoidal shape.

[0049] In a preferred form, a plurality of serpentine elements 132 maybe provided distributed substantially evenly about the periphery of theperipheral wall 126. For example, as shown in FIGS. 5A-5D, a pair ofserpentine elements 132 may be attached to the peripheral wall 126opposite one another.

[0050] Turning to FIGS. 5A-5D, a stent-graft 110 having a pair of axialserpentine elements 132 a, 132 b is shown being rolled from an enlargedcondition to a contracted condition. The exo-skeleton 114 is preferablybiased to assume the enlarged condition of FIG. 5A. Because of thespaces 133 extending substantially axially between the serpentineelements 132 a, 132 b, the stent-graft 110, including coiled-sheetstents (not shown) on the ends of the stent-graft 110, may be flattened,as shown in FIG. 5B. One edge of the stent-graft 110 may then be rolled,similar to a coiled-sheet stent, as shown in FIG. 5C, until the entirestent-graft 110 is fully rolled into the contracted condition, shown inFIG. 5D, thereby providing a reduced profile. The stent-graft 110 maythen be retained in the contracted condition to facilitate introductioninto and advancement within a patient's vasculature, until deployed at atarget treatment site, whereupon the stent-graft 110 may automaticallyexpand to its enlarged condition.

[0051] Turning to FIG. 6, another preferred embodiment of a stent-graft210 is shown, which has a substantially tapered configuration betweenits first and second ends 220, 222. Similar to the previous embodiments,the stent-graft 210 has a tubular graft 212 to which an exo-skeleton 214is attached to provide a resilient, flexible region. Coiled-sheet stents216, 218 are attached to the ends 220, 222 of the tubular graft 212 foranchoring the ends 220, 222 within a body passage. The second end 222 ofthe tubular graft 212 has a diameter that is substantially smaller thanthe first end 220 to conform substantially to the anatomy of a taperedblood vessel or to extend between a first larger vessel and a secondsmaller vessel.

[0052] Turning to FIG. 8, a tapered stent-graft 210, such as that justdescribed, may be used in a method for repairing an aortic aneurysm 250that extends from an abdominal aorta 252 through a bifurcation 254 intothe iliac arteries 256 a, 256 b. The stent-graft 210, in a contractedcondition, may be introduced across the bifurcation 254 with the largerfirst end 220 oriented towards the abdominal aorta 252. For example, thestent-graft 210 may be placed on a catheter delivery device (not shown),percutaneously introduced into a peripheral artery (not shown), advancedinto the ipsilateral iliac artery 256 a, and through the bifurcation 254until the first end 220 reaches an undamaged region of the abdominalaorta 252. The stent-graft 210 may be then deployed and expanded to itsenlarged condition, for example, when the exo-skeleton 214 automaticallyexpands upon deployment. Coiled-sheet stents 216, 218 on the stent-graft210 may be expanded to substantially seal and anchor the stent-graft 210to undamaged regions of the abdominal aorta 252 and the ipsilateraliliac artery 256 a, respectively.

[0053] The contralateral iliac artery 256 b may be substantiallypermanently occluded with a vessel occluder 260, and afemoral-to-femoral bypass graft 270 may be attached between the femoralarteries 258, or alternatively between the iliac arteries 256, to allowblood flow from the ipsilateral iliac artery 256 a into thecontralateral iliac artery 256 b and beyond.

[0054] Turning to FIG. 7, a stent-graft 310 for repairing a bifurcationis shown, in accordance with another aspect of the present invention.The stent-graft 310 includes a plurality of tubular segments, namely afirst main segment 312, a second extension segment 314 extending fromthe first segment 312, and a third segment or “docking limb” 316 that isattachable to a collar 318 on the first segment 312. The first segment312 has a first end 320 and a second bifurcated end 32 defining alongitudinal axis 224 therebetween, with the second segment 314 and thecollar 318 extending adjacent one another from the second bifurcated end322.

[0055] The first and second segments 312, 314 have first and secondperipheral walls 326, 328, respectively, which may be integrally formedtogether, or may be provided as separate wall portions that are attachedto one another. The first peripheral wall 326 defines a lumen 330 thatextends from the first end 320 through the first segment 312 and isbifurcated into a first branch lumen 330 a defined by the secondperipheral wall 328 and a second branch lumen 330 b at least partiallydefined by the collar 330 b.

[0056] An exo-skeleton 332 is attached to at least one of the first andsecond peripheral walls 326, 328 and/or the collar 318, which includes aplurality of serpentine elements 334, similar to the serpentine elementspreviously described herein. Preferably, a first set of serpentineelements 334 a are attached to the first peripheral wall 326 to supportthe first segment 312, and a second set of serpentine elements 334 b areattached to the second peripheral wall 328 to support the second segment314. The serpentine elements 334 may be individually attached to therespective peripheral walls 326, 328 and/or adjacent serpentine elementsmay be connected to one another by one or more connector elements (notshown), as described above.

[0057] A first coiled-sheet stent 336 is attached to the first end 320for substantially anchoring and/or sealing the first end 320 within abody passage. Similarly, a second coiled-sheet stent 338 is attached toa distal end 340 of the second segment 314.

[0058] The docking limb 316 has a third peripheral wall 348 to which oneor more serpentine elements 350 may be attached, thereby furtherdefining the exo-skeleton 332 of the stent-graft 310. A thirdcoiled-sheet stent 342 may be attached to a first or distal end 344 ofthe docking limb 316. A second or proximal end 346 of the docking limb316 is attachable to the collar 318 on the first segment 312, forexample, by a lap connection, or alternatively using anothercoiled-sheet stent (not shown).

[0059] The exo-skeleton 332 may be directed between a contractedcondition for facilitating introduction within a body passage and anenlarged condition for deployment within the body passage, similar tothe stent-grafts previously described herein. For example, eachserpentine element 334 a, 334 b, 350 may be radially compressible to itscontracted condition and biased to assume its enlarged condition.

[0060] In a preferred form, the first end 320 of the first segment 312has a size in its enlarged condition that corresponds substantially tothe diameter of an undamaged region of an abdominal aorta. The distalends 340, 344 of the second segment 314 and the docking limb 316 havesizes in their enlarged conditions that are substantially smaller thanthe size of the first segment 312, preferably correspondingsubstantially to the diameter of an undamaged region of an iliac artery.

[0061] The first and second segments 312, 314 may be radially compressedinto their contracted conditions and directed within a patient'svasculature to a bifurcated treatment site, such as a site of ananeurysm at the aorto-iliac bifurcation (not shown), similar to thatshown in FIG. 8. The first end 320 may be aligned with an undiseasedregion of the abdominal aorta proximate the aneurysm, with the secondsegment 314 extending into a first iliac artery and the collar 318oriented towards a second iliac artery. The first and second segments312, 314 may be deployed and expanded to their enlarged conditions, andthe first and second coiled-sheet stents 336, 338 expanded tosubstantially engage the walls of the undiseased abdominal aorta andfirst iliac artery, respectively.

[0062] The docking limb 316, in its contracted condition, may beadvanced into the second iliac artery, and the proximal end 346 alignedwith the collar 318. The docking limb 316 may then be deployed andexpanded to its enlarged condition such that the proximal end 346substantially engages the collar 318. The third coiled-sheet stent 342may be expanded to substantially seal and engage an undiseased region ofthe second iliac artery.

[0063] Thus, the damaged region of the aorto-iliac bifurcation may becompletely bypassed using a stent-graft 310 in accordance with thepresent invention. The flexible exo-skeleton 332 may allow thestent-graft 310 to conform substantially to the anatomy at thebifurcated treatment site, while supporting the tubular graft segments312, 314, 316 to provide a substantially open and unobstructed lumen toaccommodate the flow of blood therethrough. The coiled-sheet stents 336,338, 342 may substantially anchor the respective ends 320, 340, 344 ofthe stent-graft 310 and/or substantially seal the stent-graft 310 to thewalls of the vessels.

[0064] While the invention is susceptible to various modifications, andalternative forms, specific examples thereof have been shown in thedrawings and are herein described in detail. It should be understood,however, that the invention is not to be limited to the particular formsor methods disclosed, but to the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the appended claims.

What is claimed is:
 1. A stent-graft, comprising: a tubular graft havinga peripheral wall defining a periphery and a lumen therein, the lumenextending axially between first and second ends of the tubular graft; anexo-skeleton attached to the peripheral wall, the exo-skeletoncomprising one or more serpentine elements, each serpentine elementextending both peripherally and axially along at least a portion of theperipheral wall; and a stent on the first end for substantiallyanchoring the first end within a body passage.
 2. The stent-graft ofclaim 1 , wherein each serpentine element comprises a zigzag structureextending substantially peripherally about the peripheral wall of thetubular graft.
 3. The stent-graft of claim 2 , further comprising aplurality of serpentine elements distributed axially along theperipheral wall for providing articulation of the tubular graft betweenadjacent serpentine elements.
 4. The stent-graft of claim 3 , whereinthe plurality of serpentine elements are individually attached to theperipheral wall.
 5. The stent-graft of claim 3 , wherein the pluralityof serpentine elements are connected to one another by one or moreconnector elements extending between adjacent serpentine elements. 6.The stent-graft of claim 1 , wherein each serpentine element defines agenerally sinusoidal shape extending substantially axially along theperipheral wall.
 7. The stent-graft of claim 6 , further comprising aplurality of serpentine elements distributed substantially evenly aboutthe periphery of the peripheral wall.
 8. The stent-graft of claim 6 ,wherein each serpentine element includes substantially transverseperipheral elements, adjacent transverse peripheral elements beingconnected by alternating curved elements, thereby defining the generallysinusoidal shape.
 9. The stent-graft of claim 1 , wherein theexo-skeleton is directable between a contracted condition forfacilitating introduction within a body passage and an enlargedcondition for deployment within the body passage, the exo-skeletonsubstantially supporting the tubular graft to hold the lumen of thetubular graft substantially open in the enlarged condition.
 10. Thestent-graft of claim 9 , wherein the exo-skeleton is radiallycompressible to the contracted condition and biased to assume theenlarged condition.
 11. The stent-graft of claim 9 , wherein thecontracted condition of the exo-skeleton is achieved by substantiallyflattening and circumferentially rolling the exo-skeleton.
 12. Thestent-graft of claim 1 , wherein the tubular graft comprises a polymericmaterial.
 13. The stent-graft of claim 1 , wherein the polymericmaterial is selected from the group consisting of polyester,polytetrafluorethaline, dacron, teflon, and polyurethane.
 14. Thestent-graft of claim 1 , wherein the exo-skeleton is attached to thetubular graft by sutures, staples, wires, or an adhesive.
 15. Thestent-graft of claim 1 , wherein the exo-skeleton is attached to thetubular graft by a process selected from thermal bonding, chemicalbonding, and ultrasonic bonding.
 16. The stent-graft of claim 1 ,wherein the exo-skeleton comprises a flat-coiled sheet with the one ormore serpentine elements formed therein.
 17. The stent-graft of claim 1, wherein each serpentine element comprises a wire formed into aserpentine shape.
 18. The stent-graft of claim 1 , wherein the stent onthe first end comprises a coiled-sheet stent.
 19. The stent-graft ofclaim 1 , wherein the stent includes external outwardly oriented hooksfor engaging a wall of a body passage.
 20. The stent-graft of claim 1 ,further comprising prothrombotic material on an exterior surface of atleast the stent, or one of the first and second ends of the tubulargraft.
 21. The stent-graft of claim 1 , wherein the first end of thetubular graft has a cross-section that is substantially smaller than across-section of the second end of the tubular graft.
 22. Thestent-graft of claim 1 , wherein the exo-skeleton is attached to anexterior surface of the tubular graft.
 23. A stent-graft, comprising: atubular graft having a peripheral wall defining a periphery and a lumentherein, the lumen extending axially between first and second ends ofthe tubular graft; and a plurality of serpentine elements attached toand distributed axially along the peripheral wall in a predeterminedconfiguration for providing articulation of the tubular graft betweenadjacent serpentine elements, each serpentine element defining a zigzagshape extending substantially peripherally about the peripheral wall ofthe tubular graft.
 24. The stent-graft of claim 23 , further comprisinga stent on at least one of the first and second ends.
 25. Thestent-graft of claim 24 , wherein the stent comprises a plurality ofresilient mesh elements, the mesh elements being adapted to partiallyrecoil when the stent is subjected to radially compressive forces. 26.The stent-graft of claim 25 , wherein the entire stent is made ofresilient mesh elements.
 27. The stent-graft of claim 24 , wherein thestent comprises a coiled-sheet stent.
 28. The stent-graft of claim 27 ,wherein the coiled-sheet stent comprises a stretchable portion definedby a plurality of resilient mesh elements adapted to partially recoilwhen the stent is subjected to radially compressive forces.
 29. Thestent-graft of claim 28 , wherein the stretchable portion extendslongitudinally between first and second ends of the stent.
 30. Thestent-graft of claim 28 , wherein the stretchable portion comprises asleeve on an end of the coiled-sheet stent exposed beyond the respectiveend of the tubular graft.
 31. The stent-graft of claim 23 , wherein theplurality of serpentine elements are individually attached to theperipheral wall.
 32. The stent-graft of claim 23 , wherein the pluralityof serpentine elements are connected to one another by one or moreconnector elements extending between adjacent serpentine elements. 33.The stent-graft of claim 23 , wherein each serpentine element isdirectable between a contracted condition for facilitating introductionwithin a body passage and an enlarged condition for deployment withinthe body passage.
 34. The stent-graft of claim 33 , wherein eachserpentine element is radially compressible to the contracted conditionand biased to assume the enlarged condition.
 35. The stent-graft ofclaim 23 , wherein the second end of the tubular graft is bifurcated,and wherein the stent-graft further comprises: a tubular graft extensionsegment extending from the second end, the tubular graft extensionsegment having a peripheral wall; and a plurality of serpentine elementsattached to and distributed along the peripheral wall of the tubulargraft extension segment in a predetermined configuration for providingarticulation of the tubular graft extension segment between adjacentserpentine elements.
 36. The stent-graft of claim 35 , furthercomprising: a tubular graft docking limb having a peripheral wall, thedocking limb being attachable to the second end of the tubular graftadjacent the tubular graft extension segment; and a plurality ofserpentine elements attached to and distributed along the peripheralwall of the tubular graft docking limb in a predetermined configurationfor providing articulation of the tubular graft docking limb betweenadjacent serpentine elements.
 37. A stent-graft for placement within abifurcation, comprising: a first tubular graft segment having a firstend and a second bifurcated end, the first tubular graft segment havinga first peripheral wall; a second tubular graft segment extending fromthe second bifurcated end, the second tubular graft segment having asecond peripheral wall; and an exo-skeleton attached to at least one ofthe first and second peripheral walls, the exo-skeleton comprising oneor more serpentine elements, each serpentine element extending bothperipherally and axially along at least a portion of the respectiveperipheral wall to which it is attached.
 38. The stent-graft of claim 37, further comprising a stent on the first end for substantiallyanchoring the first end within a body passage.
 39. The stent-graft ofclaim 37 , further comprising a stent on the second tubular graftsegment opposite the second end of the first tubular graft segment. 40.The stent-graft of claim 37 , further comprising a third tubular graftsegment attachable to the second bifurcated end adjacent the secondtubular graft segment, the third tubular graft segment having a thirdperipheral wall.
 41. The stent-graft of claim 40 , wherein theexo-skeleton comprises one or more serpentine elements attached to thethird peripheral wall.
 42. The stent-graft of claim 37 , wherein theplurality of serpentine elements are individually attached to therespective peripheral wall.
 43. The stent-graft of claim 37 , whereinthe plurality of serpentine elements are connected to one another by oneor more connector elements extending between adjacent serpentineelements.
 44. The stent-graft of claim 37 , wherein each serpentineelement is directable between a contracted condition for facilitatingintroduction within a body passage and an enlarged condition fordeployment within the body passage.
 45. The stent-graft of claim 44 ,wherein each serpentine element is radially compressible to thecontracted condition and biased to assume the enlarged condition.
 46. Amethod for repairing an aneurysm at a bifurcation between a first mainvessel and second and third branch vessels, comprising the steps of:percutaneously introducing a stent-graft into a vessel in a contractedcondition, the stent-graft comprising a flexible exo-skeleton attachedto a tubular graft; advancing the stent-graft across the bifurcationbetween undiseased portions of the first and second vessels; expandingthe stent-graft to an enlarged condition, the exo-skeleton comprisingserpentine elements retaining a lumen of the tubular graft substantiallyopen; occluding the third vessel proximate the bifurcation; andimplanting a bypass graft between the second and third vessel downstreamfrom the bifurcation.
 47. A stretchable stent, comprising: a coiled-upsheet having overlapping inner and outer longitudinal sections, andbeing radially expandable between a first size and one or more largersizes, the coiled-up sheet defining a periphery in a plane substantiallyperpendicular to a longitudinal axis thereof; a plurality of teethextending from the inner longitudinal section for engaging openings inthe outer longitudinal section to selectively secure the coiled-up sheetin the one or more larger sizes; and a stretchable portion comprising aplurality of resilient mesh elements extending along a portion of thecoiled-up sheet, the mesh elements being adapted to partially recoilabout the periphery of the coiled-up sheet when the stent is subjectedto radially compressive forces.
 48. The stent-graft of claim 47 ,wherein the stretchable portion extends longitudinally between first andsecond ends of the coiled-up sheet.
 49. The stent-graft of claim 47 ,wherein the stretchable portion comprises a sleeve on an end of thecoiled-up sheet.
 50. The stent-graft of claim 47 , wherein the coiled-upsheet comprises Nitinol.
 51. The stent-graft of claim 50 , wherein thecoiled-up sheet is biased to adopt a second size larger than the firstsize when the Nitinol is in its austenitic phase, whereby the meshelements define a stretched configuration about the periphery of thecoiled-up sheet.
 52. The stent-graft of claim 50 , wherein the coiled-upsheet is biased to adopt a third size smaller than the second size whenthe Nitinol is in a martensitic phase, whereby the mesh elements definean unstretched configuration substantially smaller than the stretchedconfiguration.
 53. The stent-graft of claim 47 , wherein the coiled-upsheet comprises an unstretchable portion that is generallyincompressible about the periphery.